1. Field of the Invention
The present invention relates to an apparatus for and method of machining ferrule end face serving as an optical connector end. More particularly, the present invention relates to a method of high speed machining of a ferrule end face for polishing the ferrule end face in a simple manner at a high speed under various situations in various locations. Further, the present invention relates to a polishing machine, which is small in size and light in weight and available to be used at a reduced electric power consumption, for realizing the high speed end face machining method for the ferrule.
In the present invention, an applicable polish object mainly comprises a 1.25 mm diameter ferrule, which has a small polishing surface area. Additionally, it is possible to achieve more higher-density interconnections by using the 1.25 mm diameter ferrule.
2. Description of the Related Art
FIGS. 1A to 1D show pre-treatments of the related art ferrule end face polishing process and typically show working strokes between fiber bonding and surface alignment between the fiber and the ferrule.
Firstly, as shown in FIG. 1A, a fiber 200 is inserted through and bonded to a ferrule 100, and the fiber 200 protrudes from a polishing objective end face G of the ferrule 100. In this process, the adhesive is applied to the polishing objective end face G of the ferrule 100, thereby forming an adhesive layer 300. Also, although a thickness of the adhesive layer 300 depends on the diameter of the ferrule 100, it is to be noted that the smaller the diameter of the ferrule 100, the more difficult will be the bonding work to be performed in an accurate fashion.
Then, as shown in FIG. 1B, a protruding portion 200a of the fiber 200 is cut at a position near the adhesive layer 300 by hand work.
During this work, an end of the fiber 200 tends to protrude to some extent in the order of 0.1 mm in distance from the adhesive layer 300.
Under such a condition, polishing is progressively performed (shown in FIG. 1C) to perform machining to allow the polishing objective end face G of the ferrule 100 to line on the same plane as a polishing objective end face 200b of the fiber 200 (as shown in FIG. 1D). This step is termed adhesive removing step or first step. The fiber 200 is protected with the adhesive layer 300 during first step.
Conventionally, in order to achieve a remarkable amount of processing in a short time period during first step using a polishing film (not shown) with a relatively large grain size. For this reason, during an initial stage of processing of first step, a concentrated force applies to the protruding portion 200a of the fiber 200, thereby a part of the fiber 200 is bent with a bent end being folded into the adhesive layer 300. However, due to the presence of the adhesive layer 300, no probability occurs where such a folded piece reaches the ferrule 100, and the folded piece remains in the adhesive layer 300.
After first step has been terminated, the polishing objective end face 200b of the fiber 200 lies on the same plane as the polishing objective end face G of the ferrule 100. That is, the adhesive layer 300 plays a role to protect a distal end (the polishing objective end face 200b) of the fiber 200 during processing.
Also, the polishing objective end face 200b of the fiber 200 lies on the substantially same plane as the polishing objective end face G of the ferrule 100, and serves as a surface suited for subsequent polishing process (not shown). Since, in general, the surface resulted by processing in first step is polished with the relatively coarse abrasive grain, the resulting surface has a coarse grade to some extent.
After first step, the end face is processed in a convex spherical shape (in coarse processing step, i.e., second step) and finishing (third step) is performed for the purpose of enhancing a return loss and suppressing intrusion of the fiber.
The connector end face (now shown) resulting from the process up to third step has a cross sectional shape formed in a convex spherical surface with a radius of curvature falling in a range of approximately 10 mm to 25 mm. Also, it is required for the optical connector end face to have a process precision that is required to fall in a deviation between an apex of the convex sphere and a center of the fiber 200 at a value less than 50 μm while the amount of intrusion of the fiber 200 with respect to the ferrule falls in a range of 0.05 μm to 0.1 μm. In case of a small size ferrule such as Type MU connector, it is difficult to machine the ferrule so as to satisfy the above-described conditions in respect of the amount of deviation between the apex of the convex sphere and the center of the fiber 200.
Major factors for difficulties are attributed to 1) a probability where, in case of a small size ferrule, an adhesive coating surface, that is, the polishing objective end face G of the ferrule 100, are extremely small in area whereby adhesive spreads over a ferrule tapered surface 100a shown in FIGS. 1A, and 2) another probability where, if adhesive spreads over the other area, such as the ferrule tapered surface 100a, than the polishing objective end face G of the ferrule 100, the center of the polishing objective end face G is displaced from the center of the fiber 200 whereby decentering takes place in the related art maching method where the convex spherical surface is formed using rubber resilient deformation of a polishing table.
Further, with the ferrule 100 such as type MU ferrule, when machining the ferrule 100 so as to realize a curvature of the convex sphere surface that satisfies a specification, a difference in an amount, that has been processed, between a central portion and an outer peripheral part of the ferrule is minute with a resultant ease of occurrence of decentering. For this reason, in general, a high precision polishing machine is needed.
An apparatus for performing such high precision machining is required to trace an idealistic moving orbit and has a moving precision of the apparatus. An idealistic orbit is drawn in a case where the moving orbit of the polishing table describes a perfect circle with respect to the polishing objective end face of the optical connector (ferrule). In such a case, it is possible to obtain an optical connector with a desired polishing objective end face.
The polishing table is made of a resiliently deformable member, and the polishing table is configured to resiliently deform in case the polishing objective end faces of the ferrule and the fiber are brought into contact with the polishing table, deformation occurs in an area in which the polishing table is brought into contact with the polishing objective end faces. Rotating the polishing table under such a condition, a convex spherical surface is formed. When this takes place, if processing is performed on the idealistic moving orbit, a processing pressure distribution, caused by rubber resilient deformation resulting from the ferrule end face and the fiber being indented into the polishing table, is uniform, with resultant formation of convex sphere surfaces with less degree of decentering.
With an actual polishing machine, a position in which the ferrule is mounted is preliminarily fixed, and the polishing table revolves and draw a perfect circular orbit about a center of the position that is separated from the fixed position of the ferrule by a given displacement value.
However, when attempting to performing polishing through only revolving motion of the polishing table, only an identical single point of the polishing film on the polishing table is used and a polishing capability of the relevant area becomes lower than that of the other area of the polishing film. Replacement of the polishing film with a largely remaining non-used area arises an issue to be of non-economic.
Therefore, in order to efficiently use the polishing film, it has been a usual practice for the polishing table to trace the perfect circular orbit while progressively shifting the revolving center.
Thus, in order to realize complex and highly accurate motion of the polishing table, it has been a usual practice for the related art to take a method of using a cam linkage mechanism and a method of using a sliding stage. However, such a related art technology requires a complex rotation and a high power output.
Accordingly, there are many related art machining machines that are large in size and large in weight in each of which batch processing is executed for a large number of ferrules to minimize a work time and cost for each ferrule terminal.
Further, with a conventional polishing machine of a portable type that is light in weight and low in cost, there are many probabilities where the polishing machines are of the type which are insufficient in the polishing orbit with the use of arm's rocking movement with a resultant issue in which the above-described conditions are not satisfied.
It is, therefore, an object of the present invention to provide a machining apparatus that is able to perform polishing work at various locations involving outdoor locations and to perform polishing work in a short time period in an easy fashion at a low cost without a need for particular skills of workers.